538© IJMDC. https://www.ijmdc.com
International Journal of Medicine in Developing Countries
Evaluation of the location of mental foramen by cone-beam computed tomography for patients visiting dental clinics at Qassim UniversityAbdulsalam Saleh Alharbi1*, Hatim Saeed Almutairi1, Abdulmajeed Fahad Albishri1, Shaul Hameed Kolarkodi2
ABSTRACT
Background: The mental foramen (MF) is located bilaterally on the anterior surface of the mandible. It is usu-ally seen between the roots of the first and second mandibular premolars. It is challenging to locate the MF clinically; the knowledge of the exact location of the MF is vital before placing implants to achieve effective mental nerve block anesthesia. Hence the current study was aimed at evaluating the location of MF by Cone-Beam computed tomography (CBCT) for patients visiting dental clinics at Qassim University.
Methodology: The study sample of 43 CBCT images, with MF visible on both sides of the mandible, was selected from achieves, with age groups ranged 20-60 years. After determining the horizontal and vertical diameter of each MF, a ratio of both diameters (H:V) was calculated and used to classify the form of MF into one of three types: Type I (oval horizontal form), Type II (oval vertical form), and Type III (round form). The location of the MF was noted. The variables were statistically analyzed using Statistica 12.5 PL software (StatSoft, Poland).
Results: The current study revealed that the most frequent anterior-posterior position of the MF on both the right and left sides in female and male subgroups was a location between the first and second premolar. While the most frequent superior-inferior position of the MF was below the apices of the first and second mandibular premolar teeth roots. Type II MF was the most rarely observed type in a whole studied population.
Conclusion: The current study showed that CBCT analysis for the type and location of MF could contribute to the success of implant planning and to avoid future complications.
Keywords: Cone beam computed tomography, mental foramen, implant dentistry.
Introduction
The mental foramen (MF) is a bilateral opening localized
on the anterior surface of the mandible. Most often,
it is situated between the first and second inferior
premolars. It is crucial and challenging to locate MF
by clinical procedures. Knowing the exact location
of the MF is vital for placing implants and effective
mental nerve block anesthesia. One of the complications
during implant placement in the anterior mandible is a
neurosensory alteration in the chin and lower lip due to
improper identification and protection of the MF and
anterior mental loop. In this method, using a cone-shaped
ionizing radiation beam, the high-resolution cross-
sectional three-dimensional (3D) images in the frontal,
sagittal, and transverse planes are provided by CBCT. It
can help to obtain detailed information on structures of
the maxillofacial complex and enables identification and
precise evaluation of the anatomical variations.
Knowledge of the precise location and well-defined
shape, size, and number of MF are crucial for different
clinical dental procedures. Successful and complication-
free dental procedures such as curettage, root canal
Correspondence to: Abdulsalam Saleh Alharbi*College of Dentistry, Qassim University, Al-Qassim, Saudia Arabia.Email: [email protected] list of author information is available at the end of the article.Received: 16 December 2020 | Accepted: 29 December 2020
Abdulsalam Saleh Alharbi et al, 2021;5(2):538–544.https://doi.org/10.24911/IJMDC.51-1608148826
ORIGINAL ARTICLE
Evaluation of the location of mental foramen by cone-beam computed tomography
539
treatment, periapical surgery, orthognathic surgery, and
effective anesthesia during nerve blocks depend on an
operator's knowledge about MF [1]. Implant placement
in the inter-foramina area is strictly related to the MF
location because it determines the position of the most
distal implants. Many studies indicate that a minimum
distance between MF and an implant should amount to
6 mm [2,3]. Any invasive procedure performed in this
region may damage the neurovascular bundles and cause
serious complications such as paresthesia [4].
So far, it is known that the MF position depends on the
ethnic origin of the patients [5]. A location and number
of MF can be evaluated with different methods such as
macroscopic investigations on dry skulls [6,7], plane
radiographs [8,9], and computed tomography (CT)
images [10]. Among several methods, the most accurate
and safest method for patients is currently considered to
be the cone-beam computed tomography (CBCT) study.
In this method, a cone-shaped ionizing radiation beam
is used to obtain the high-resolution cross-sectional
images in the front, sagittal, and transverse planes
[11,12]. Moreover, CBCT is a cheaper test than classical
CT and requires a significantly lower ionizing radiation
dose [13,14]. CBCT provides three-dimensional (3D)
images, which can help to obtain detailed information
on structures of the maxillofacial complex, and enables
identification and precise evaluation of the anatomical
variations [15,16]. Hence, this study aimed to determine
the size and location of MF in relation to the lower teeth
using CBCT.
Material and Methods
Following ethical approval, 43 CBCT images were
selected from the Qassim University Dental Clinics.
CBCT images were selected according to the following
inclusion criteria: age groups range 20-60 years inclusive,
MF visible on both sides of the mandible, all mandibular
premolar teeth present, and premolar region visible on
the CBCT image. The CBCT images were selected from
the CBCT archive and communications system by a
dental and maxillofacial radiology staff member so that
only radiographs of grade one quality were included. The
exclusion criteria were images with large pathological
lesions in the mandible, bone fractures in regions of
examination, inadequate picture quality caused by
osteosynthesis plates/implants, or patient movement
during exposure were rejected. According to the above
inclusion and exclusion criteria, the resulting group of
43 patients (20 males and 23 females) was used in the
retrospective analysis. The characteristics of the study
group were presented in Table 1 and Figure 1.
All CBCT images were performed using the CALILEOS
device at 120 kVp and 5.0 mA, with a voxel size 0.125-0.25
mm and an exposure time of 20 seconds. All images were
analyzed using specialized computer software (Sirona
Dental System GmbH & Co. KG, Bonn, Germany). Three
independent researchers manually evaluated the images.
Each measurement of a single image was performed twice
separately for the left and right sides. Average values from
measurements of both researchers were calculated and
used for further analysis. Measurements were performed
on axial, sagittal, and coronal CBCT slices of 0.13 mm
thickness. The vertical size of MF (V) was determined on
the cross-sectional CBCT images, and the horizontal size
of MF (H) was assessed on axial scans (Figure 1). After
determining the horizontal and vertical diameter of each
MF, a ratio of both diameters (H:V) was calculated. The
ratio was used to classify the form of MF into one of three
types: Type I (oval horizontal form) was recognized when
H:V was over 1.24, Type II (oval vertical form) at H:V
value less than 0.76, and Type III (round form) when 0.76
≤ H: V ≥ 1.24 [17,18].
Horizontal relationships between MF and roots apices of
the lower premolars and molars were classified into six
types, as shown in Figure 2. Into three types, as shown in
Figure 3 [25].
In Introduction Section, MF was located above the level
of the apices of the first and second mandibular premolar
teeth. In Material and Methods Section had MF at the
level of the apices of the first and second mandibular
premolar teeth, whereas, in Results Section MF was
located below the level of the apices of the first and
second mandibular premolar teeth.
The variables were statistically analyzed using Statistica
12.5 PL software (StatSoft, Poland). The Kruskal-Wallis
test was used to evaluate a relationship between the
vertical and horizontal size of MF and the age of patients,
and the Mann-Whitney U test was used to evaluate the
relationship between horizontal and vertical diameters of
MF and sex of the patients. The chi-square test was used
Table 1. Characteristics of the study group.
Age of patients (years)
GenderTotal NMale Female
N % N %20-27 9 45.0 12 52.2 21
28-60 11 55.0 11 47.8 22
Total 20 100.0 23 100.0 43
Figure 1. Cross sectional images of CBCT showing horizontal and vertical measurements of mental foramen.
Evaluation of the location of mental foramen by cone-beam computed tomography
540
to evaluate the relationship between the type of MF and
age and sex of the patients. The statistical significance
was established at p < 0.05.
Results
In the current study, there were no significant differences in
values of the vertical diameters and the H:V ratio on both
sides in relation to the age of participants. However, there
was a significant difference in the value of the horizontal
diameter on the right side in relation to the participant's
age. Comparison of the average values of the horizontal
diameters between male and female subgroups revealed
significant differences both on the right and left sides.
However, a comparison of the average values of the vertical
diameters between male and female subgroups revealed
significant differences on the left side, as shown in Table 2.
In males, the average values of a horizontal diameter (p = 0.049) were significantly higher on both right and left
sides than in the female subgroup, whereas on the left side,
the average value of the vertical diameter was significantly
higher in men (p = 0.031) as compared to women.
Figure 3. Schematic representation of the MF's superior-inferior position in relation to the lower premolars (PM1, first premolar; PM2, second premolar). Position (1) above the roots apices of PM1 and PM2, (2) at the level of the roots apices of PM1 and PM2, (3) below the roots apices of PM1 and PM2.
Table 2. Comparison of a MF size in the studied subjects.
Subgroup
Right side Left sideHorizontal
diameter (mm)Vertical
diameter (mm) H:V Horizontal diameter (mm)
Vertical diameter (mm) H:V
Mean ± SD (min-max)
Mean ± SD (min-max)
Mean ± SD (min-max)
Mean ± SD (min-max)
Mean ± SD (min-max)
Mean ± SD (min-max)
Age (years)
20-274.07 ± 0.99 3.50 ± 0.67 1.18 ± 0.29 4.38 ± 0.93 3.56 ± 0.77 1.25 ± 0.22
(2.86-6.16) (2.28-5.33) (0.70-1.73) (2.46-6.44) (2.16-5.46) (0.75-1.65)
28-603.57 ± 0.71 3.47 ± 0.67 1.07 ± 0.29 3.76 ± 0.74 3.66 ± 0.79 1.06 ± 0.24
(2.34-4.86) (2.01-5.33) (0.67-1.67) (2.75-4.95) (2.81-6.15) (0.47-1.72)
p value .048 .815 .982 .524 .966 .871
Gender
Male 3.84 ± 1.06 3.53 ± 0.81 1.12 ± 0.31 4.14 ± 1.07 3.89 ± 0.92 1.09 ± 0.25
(2.34-6.16) (2.01-5.33) (0.67-1.67) (2.75-6.44) (2.53-6.15) (0.47-1.65)
Female3.78 ± 0.72 3.44 ± 0.51 1.13 ± 0.28 3.99 ± 0.70 3.38 ± 0.54 1.20 ± 0.24
(2.84-5.25) (2.28-4.45) (0.70-1.73) (2.46-5.19) (2.16-4.71) (0.75-1.72)
p value 0.049 0.183 0.588 0.041 0.031 0.819
Figure 2. Schematic representation of the MF's anterior-posterior position in relation to the lower teeth (I1, central incisor; I2, lateral incisor; C, canine; PM1, first premolar; PM2, second premolar; M1, first molar). Position (1) between the C and PM1, (2) in line with the long axis of the PM1, (3) between the long axes of the PM1 and PM2, (4) in line with the long axis of the PM2, (5) between the long axes of the PM2 and M1 and, (6) in line with the long axis of the mesial root of the first lower molar.
Evaluation of the location of mental foramen by cone-beam computed tomography
541
There were no significant relationships between age
and gender of the patients (p > 0.05) and type of MF on
the right and left sides, as shown in Table 3. However,
it is worth noting that Type II MF was the most rarely
observed type among the whole studied population.
The most frequent anterior-posterior position of the
MF on both the right and left sides in female and male
subgroups was between the first and second premolar, as
shown in Table 4.
The most frequent superior-inferior position of the MF
on both the right and left sides was below the level of the
apices of the first and second mandibular premolar teeth
roots, as shown in Table 5.
Discussion
In the current study, the shape, size, and position of the
MF were evaluated in the patients who visited dental
clinics of Qassim University to take CBCT. According
to the size of MF, no differences with relation to the age
of the subjects were observed except for the horizontal
diameter on the right side. On the other hand, statistically
significant differences were observed in the size of MF in
relation to the sex of the patients. In men, the horizontal
diameter on both sides of the mandible and vertical
diameter on the left side was higher than those observed
in women. The results were consistent with those found
by Ewa et al. [19], Gungor et al. [20], Zhang et al. [18],
and Kalender et al. [21], in which the horizontal and
vertical diameters also evaluated in the CBCT study were
higher in men in comparison to women. In our research,
the values of the horizontal and vertical diameters seem
to be higher than in Turkey assessed using the CBCT
method [20] as well as in Bosnia [7] and Sri Lanka [22],
where the studies on human mandibles were performed.
In contrast, the values were lower than those observed
in the Chinese population in CBCT studies [18]. It can
confirm the thesis about differences in the size of MF
between different ethnic groups.
Table 3. Comparison of a MF type in the studied subjects.
SubgroupMF type - right side MF type - left side
I II III I II IIIN (%) N (%) N (%) N (%) N (%) N (%)
Age (years)
20-27 8 (38.1) 1 (4.7) 12 (57.1) 9 (42.9) 1 (4.7) 11 (52.4)
28-60 7 (31.8) 4 (18.2) 11 (50.0) 3 (13.6) 1 (4.5) 18 (81.8)
p value 0.389 0.097
Gender
Male 8 (40.0) 3 (15.0) 9 (45.0) 3 (15.0) 1 (5.0) 16 (80.0)
Female 7 (30.4) 2 (8.7) 14 (60.9) 9 (39.1) 1 (4.3) 13 (56.5)
p value 0.563 0.211
Table 4. Comparison of the horizontal location of the MF in relation to the gender of the patients.
Right side Left side2 N (%) 3 N (%) 4 N (%) 1 N (%) 2 N (%) 3 N (%) 4 N (%) 5 N (%)
M 3 (15.0) 15 (75.0) 2 (10.0) 0 (0.0) 1 (5.0) 17 (85.0) 2 (10.0) 0 (0.0)
F 4 (17.4) 12 (52.2) 7(30.4) 1 (4.3) 7 (30.4) 9 (39.1) 5 (21.7) 1 (4.3)
Evaluation of the location of mental foramen by cone-beam computed tomography
542
Evaluation of the ratio of the two diameters was helpful in
the assessment of the shape of MF. In our study, the most
frequent shape was the round shape (Type III), whereas
the next most frequent was the oval horizontal shape
(Type I). Our observations correspond to those obtained
by Sankar et al [23]. in the Indian population in the studies
on human mandibles, similarly to findings noticed by
Sekerci et al. [24] in the Turkish population and Alam et
al. in the Arabic population in CBCT studies [25].
However, the oval horizontal shape was the most
frequent form in the Chinese population during the
CBCT studies found by Zhang et al. [18] and Ewa et
al. in the Polish population [14]. The same results were
found by Ilayperuma et al. in the Sri Lanka population in
studies on human mandibles [22] as well as Voljewica et
al. in the Bosnian population in human mandibles [7]. It
seems, therefore, that not only the size but also the shape
of the MF is heterogeneous among different populations.
In our study, the superior-inferior position of the MF
below the level of the apices of the first and second
mandibular premolar teeth roots was the most frequent
location, regardless of gender and age on both the left
and right sides. The second most frequent position of the
MF found in our patients was a location at the level of
the apices of the first and second mandibular premolar
teeth roots. The results were similar to those obtained by
Sekerci et al [24]. in CT studies and other researchers
[25,26,19] using both CBCT and panoramic radiographs
methods.
In the anterior-posterior position, the most frequent MF
location regardless of the gender of the subjects was a
position between the first and second premolars of the
mandible characteristic for older patients and, next, a
location in the long axis of the second premolars of a
mandible, typical for the youngest patients on the right
side. Our studies correspond with the results of the
research carried out in every case using CT methods
by Ewa et al. [14], Sekerci et al. [24], and Kalender et
al. [21] in the Turkish population. In Gungor et al. [20]
an MF position between the first and second premolars
was found to be the most typical location in women.
However, Voljevica et al. [7] observed in the patients in
Bosnia, the most frequent MF position on the right side
were in the long axis of the second premolar and on the
left side between the first and the second premolars of
the mandible.
In the studies performed by Igbigbi and Lebona
in Malawians [27], and Mbajiorgu et al. [28] in
Zimbabweans both on human mandibles and also by
Alam et al. [25] in the Arabic population in CBCT, the
most common MF position was in the long axis of the
second premolar. The same results were obtained for the
Chinese [29], Nigerian [30], Saudi [31], Kenyan [32],
Kurdish [8], and Sri Lankan [22] populations in studies
on human mandibles and based on Orthopantomography
(OPG) and oblique lateral radiographs. However, Santini
and Land in the British population in studies on human
mandibles [33], Al-Khateeb et al. [26] in the northern
regional Jordanian population [26], and Kqiku et al.
[34] in the Kosovarian population in the studies based
on OPG radiographs found the most frequent location
of MF between the first and second premolars of the
mandible.
Table 5. Comparison of the vertical location of the MF in relation to the gender of the patients.
Right side Left side2 N (%) 3 N (%) 2 N (%) 3 N (%)
M 1 (5.0) 19 (95.0) 1 (5.0) 19 (95.0)
F 9 (39.1) 14 (60.9) 10 (43.5) 13 (56.5)
Evaluation of the location of mental foramen by cone-beam computed tomography
543
Therefore, it seems that there is no single and universal
pattern of MF location in different populations.
This makes a precise assessment of the MF location
characteristic for every population as very helpful in
clinical dental practice. The determination of the shape,
size, and position of the MF is critical, considering
numerous dental procedures carried out in the mandible.
Thus, obtained results could be beneficial for many
clinicians.
However, this study's limitation seems to be a lack of
assessment of a distance of an upper limit MF from the
alveolar crest edge and the distance of an MF lower limit
from the lower edge of a mandible.
Conclusion
The current study showed that CBCT analysis for the
type and location of MF could contribute to the success of
implant planning and avoidance of future complications. Since the sample size taken in our research was small,
we recommend research in this area with a larger study
group in the future.
List of Abbreviations
MF Mental ForamenCBCT Cone-Beam Computed tomographyOPG Orthopantomography
Conflict of interestThe authors declare that there is no conflict of interest regarding the publication of this article.
FundingNone.
Consent to participateInformed consent was obtained from all the participants.
Ethical approvalEthical approval was granted by the Ethics Committee of College of Dentistry, Qassim University via reference/letter number #: EA/6046/2019 dated.
Author details Abdulsalam Saleh Alharbi1, Hatim Saeed Almutairi1, Abdulmajeed Fahad Albishri1, Shaul Hameed Kolarkodi2
1. College of Dentistry, Qassim University, Al-Qassim, Saudia Arabia
2. Department of Maxillofacial Surgery and Diagnostic Science, College of Dentistry, Qassim University, Al-Qassim, Saudia Arabia.
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